Shear-dependency of the predicted ideal hematocrit

Area of Science:

• Hematology
• Biophysics
• Sports Science

Background:

• The ideal hematocrit (Hct) maximizes the Hct/viscosity (h/η) ratio.
• Quemada's equation predicts this optimal Hct from viscometric measurements.
• Previous studies used high shear rates (1000 s⁻¹), but curve shape depends on shear rate.

Purpose of the Study:

• To investigate the influence of varying shear rates (1–6000 s⁻¹) on the optimal Hct/viscosity curve.
• To analyze the discrepancy between theoretical and actual optimal values across shear rates.
• To determine the optimal shear rate for assessing blood viscosity and ideal hematocrit.

Main Methods:

• Viscometric measurements of blood from 11 young recreational athletes.
• Analysis of the Hct/viscosity (h/η) curve across a wide range of shear rates (1–6000 s⁻¹).
• Application of Quemada's equation to predict optimal hematocrit and h/η values.

Main Results:

• Predicted optimal h/η and Hct values increase with increasing shear rate.
• The discrepancy between predicted and actual optimal values decreases at higher shear rates, becoming asymptotic above 500 s⁻¹.
• The minimal discrepancy was observed at a shear rate of 2720 s⁻¹.

Conclusions:

• Blood viscosity measurements should be conducted at shear rates ≥ 500 s⁻¹ for accurate assessment of h/η.
• Higher shear rates provide a more reliable determination of the theoretical ideal hematocrit.
• Understanding shear rate dependency is crucial for interpreting hemorheological parameters in athletes.